Fluoropolyether lubricants are of particular interest in lubricating magnetic recording media. These lubricants are uniquely suited to form lubricant topcoats on magnetic media because of such properties as chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on magnetic recording media.
Commercially available PFPE lubricants include Krytox from DuPont, Demnum from Daikin Industries and Fomblin Z and Y fluids from Montedison. Many of the commercial PEPE lubricants are substituted with 14 polar end-groups, such as one or more hydroxyl, or carboxylic acid groups. The polar end-groups are considered necessary to improve adhesion of the lubricants to the surface of a magnetic recording medium. Several fluorinated polyakylether amides have recently proven useful in forming lubricant topcoats on magnetic recording media
These lubricants can be conventionally prepared by combining an acid chloride with an amine. For example, U.S. Pat. No. 4,897,211 discloses the preparation of a synthetic magnetic recording lubricant by reacting a perfluoropolyalkylether acid chloride with an amine at elevated temperatures to produce the amide. This method, however, requires the use of air and moisture sensitive acid chlorides. Further, acid chlorides of fluoropolyether lubricants are not readily available, thus necessitating an additional step for their preparation prior to their reaction with the amine compound to form the amide.
Lower weight fluorinated compounds have also been used for the synthesis of lower weight fluorinated alkyl amides. See, e.g., U.S. Pat. Nos. 2,502,478 and 2,523,470 which are directed to the preparation of amide derivatives of tetrafluorosuccinic acid. These preparations, however, are not related to the synthesis of polymeric fluoroyalkylether amides and the products discloses therein are not useful as lubricants for magnetic recording media. Further, it is believed that the preparations used in synthesizing low weight amides are not amenable to preparing polymeric fluoropolyalkylether lubricants.
Other preparations of amides includes reacting fluorinated compounds with ammonia as in U.S. Pat. Nos. 2,862,024 and 3,544,618. These references disclose reaction conditions that require low temperatures to produce the amides. Further the disclosed compounds are not related to magnetic recording media lubricants such as fluoropolyalkylether amides.
The preparation of fluorinated amides as intermediates in the formation of nitrites have further been disclosed, as in U.S. Pat. Nos. 5,637,748 and 5,717,037. As discussed in the 5,637,748 patent to Hung, the solubility of fluorinated compounds are typically low, thus requiring special procedures and/or handling to achieve high yield products. It is believed that these difficulties are exacerbated when preparing high molecular weight compounds, such as polymeric fluoroalkylethers. Additionally, these references, as others in the art disclose that the preparation of the amides from ammonia require low temperatures.
Accordingly a continuing need exists in the magnetic lubrication art to produce fluoropolyalkylether derivatives in direct and economical means from commercially available products. In particular a need has been demonstrated to synthesize fluorinated amides useful in magnetic recording lubrication without the use of air sensitive intermediates and/or harsh reaction conditions.